Effective use of electric power is required for recent global warming tendency. Secondary batteries for power storage are expected as one means, and from the standpoint of prevention of air pollution, early practical application of large secondary batteries is expected as an automobile power source. Further, a demand of small secondary batteries has been steadily increasing especially in association with spread and performance enhancement of electrical devices, such as digital cameras and mobile phones, as back-up sources of computers and power sources of small household electrical appliances.
As these secondary batteries, a secondary battery having performance corresponding to a device to be used is required, and typically, lithium ion batteries are mainly used.
In the lithium ion battery, a negative electrode material formed such that a negative electrode active material of graphite, or the like is fixed to a negative electrode substrate made of copper foil in a metal packaging can of aluminum, iron, or the like, a positive electrode material formed such that a positive electrode material of lithium nickel oxide, lithium cobalt oxide, or the like is fixed to a positive electrode substrate made of aluminum foil, a current collector made of aluminum or copper, a separator made of resin film, such as a polypropylene porous film, an electrolyte solution, an electrolyte, and the like are enclosed.
By the way, establishment of measures against environment pollution with used lithium ion batteries is strongly required for the expanding demand of lithium ion batteries, and recovery and effective use of valuable metals have been examined.
As a method of recovering valuable metals from a lithium ion battery provided with the above-described structure, dry treatment or incineration treatment described in Patent Literatures 1 and 2 are used. However, these methods have such drawbacks that consumption of thermal energy is large, lithium and aluminum cannot be recovered.
Furthermore, as described in Patent Literatures 3 and 4, methods of recovering valuable metals by wet treatment have been proposed. However, in such methods in which a wet treatment is used, dry treatment is partly used and keeping the costs of such methods low is difficult because of complexity of a treatment process. Therefore, the valuable metals cannot be efficiently recovered.
In particular with respect to lithium as a valuable metal, there is also a problem that impurities, such as phosphorus and fluorine, are mixed in, and thus high-quality lithium cannot be efficiently recovered in the form of a simple substance. Namely, a lithium ion battery contains, as an electrolyte, lithium hexafluorophosphate (LiPF6) and the like, which comprises a valuable metal (lithium). LiPF6 may undergo a hydrolysis reaction through wet treatment, and form a precipitate in the forms of lithium phosphate and lithium fluoride, and thus lithium cannot be efficiently recovered in the form of a simple substance.